I have a Valero with a 1986 Yamaha ProV150. I just bought it at the
end of last season and over the winter I had the impeller changed just to
be safe. Now I am overheating even when running slow (25 mph) with the
trim all the way down. It did not overheat last year.

I have removed both thermostats - they are clean and function perfectly
when I dip them in hot water.

I removed the 2 inch oval cover plate at the back of the motor at the
bottom where there is a hose attached. Inside there is a spring and
a rubber/plastic valve. ( I do not know what this is for but it is
clean and seems to function properly except that I found a loose chip of
plastic about 1/8" by 1/4" this could be nothing).

There is a water pressure gauge and the pressure is good when I start out
cold but then after about 5to10 minutes the buzzer goes off and I look
down to see the pressure is at zero. If I leave it to cool for
30mins and then start it up again the pressure is back to normal.
There is always water pissing out of the back of the engine even when the
gauge is at zero. It will also cool down in about 2 minutes if I
leave it at idle while the buzzer is going.

What should I check next?
I can't take it to the shop due to finances so my choice is fix it myself
or don't drive it. (The later may be best due to gas prices anyway.)

I look forward to hearing from you,

Thank you,
Kevin

Kevin,

You've done most of the checks and all seems fine. At this point I'd
change the entire waterpump assembly. The plate and cup can warp or have
grooves that will cause the overheat problem. Make sure you run with the
thermostats installed as the motor will overheat without them in. The
water flow is too fast with them out and the block can sometimes not be
able to get rid of its heat. For a check you can install a hose fitting on
the top of the block (fitting is facing up, one on each bank) and watch
the water flow from the engine. If you have air pockets that burp out all
the time then we'll have to search deeper. Buy a complete waterpump kit
and start there.

Keep cool, (couldn't resist)

Randy

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